1. Field of the Invention
The present invention relates to devices for monitoring around a vehicle in which target extraction is carried out by subjecting an image captured by an infrared camera device to a binary thresholding method.
2. Description of Related Art
Devices for monitoring around a vehicle have been proposed in which objects that may collide with the vehicle, such as pedestrians, are extracted from a picture around the vehicle captured by an infrared camera, and such information is supplied to a driver of the vehicle. In these devices, the probability that the vehicle will hit an object, such as a pedestrian, is calculated based on the relative distance between the vehicle and the object, and the relative speed of the vehicle.
An example of such devices for monitoring around a vehicle which extract an object, which may collide with the vehicle, from an image around the vehicle captured by an infrared camera is as follows. That is, in the device, the captured infrared image is subjected to a binary (2-level) thresholding process, and an area to which bright (white) portions are concentrated is searched for. Then, it is determined whether the area is a head portion of a pedestrian by using the aspect ratio (ratio of length to width) and the sufficiency rate of the area, and further calculating the distance between the vehicle and the area using the actual surface area and the position of the center of gravity in the image. If the area of the head portion of a pedestrian is determined, an area which forms the body of the pedestrian is determined by calculating the height of the pedestrian in the image based on the distance between the area determined to be the head portion and the camera, and an average height of an adult. These areas are displayed to be distinguished from the other regions of the image. In this manner, the position of the entire body of the pedestrian in the infrared image is determined, and this information is displayed for the driver so as to effectively assist the vision of the driver (refer to Japanese Unexamined Patent Application, First Publication No. Hei 11-328364, for example).
However, using the thresholding method, only the head portion, a part of the head portion, or the entire or only an upper half or a lower half of the body, of a pedestrian may be extracted from an infrared image, depending on the effects of a hat or clothing the pedestrian is wearing, or of the environment surrounding the pedestrian, and thus the shape of the pedestrian obtained by the binary thresholding method becomes ambiguous. Also, when a vehicle is running, due to the influence in change in the shape of a road ahead, or the pitting of the vehicle, the height of a pedestrian, from a child to an adult, is generally detected to be different from his/her real height.
Accordingly, since the barycentric coordinates of targeted objects, such as pedestrians, in the picture cannot be fixed with respect to the distance. Therefore, it is not possible to extract the targeted objects stably such as pedestrians which may collide with the vehicle, if the extraction is carried out based on the shape of at least the pedestrians' height, head, body as in the above-mentioned conventional device.